Project Summary/Abstract After decades of advances in medical imaging, x-ray based imaging modalities are still the backbone of modern day general and targeted diagnostic imaging. With the advent of flat panel detector technology, flat panel x-ray imagers (FPXIs) are now widely used in digital X-ray imaging, specifically for digital radiography, fluoroscopy, digital tomosynthesis, image-guided radiation therapy, and cone bean computed tomography. Commercial FPXIs are based on scintillators and rely on indirect conversion of x-rays to photons and then to electronic signals or are based on amorphous-Se semiconductor films that directly convert absorbed x-rays to electronic signal. The indirect FPXIs have high detective quantum efficiency (DQE) over the energy range of interest (up to 140kVp) and are used in most of the FP imaging applications. However, due to the isotropic propagation of light in the scintillators, these systems lack the necessary spatial resolution that is needed for other imaging applications. On the other hand, a-Se based panels have excellent spatial resolution and DQE, but only up to 40kVp, due to low absorptivity of a-Se at higher energies. Thus, the use of direct conversion FPXIs is currently limited only to soft-tissue applications. In this program, we will be developing direct conversion FPXIs with a novel photo-detecting polycrystalline semiconductor demonstrating high attenuation coefficient and excellent charge transport properties. This semiconductor is deposited by a low-temperature and low-cost process. The first phase of this program will focus on the optimization of the semiconductor sensor layer structure, polycrystalline film deposition parameters and device performance. By the end of this program we expect to have a fully functional prototype of the low-dose low-cost direct FPXI, suitable for transitioning to pre-clinical testing.